Schizophrenia is a complex disorder characterized by the fragmentation and disorganization of cognition and behavior. Patterns of cognition and behavior emerge from organized sequences of individual cognitive and behavioral elements. Methods derived from nonlinear dynamical and complex physical systems have revolutionized the analysis of experimental data and allow for the quantitative assessment of complex cognitive and behavioral patterns. A two-choice guessing task is a simple behavioral paradigm that can be used to experimentally obtain sequences of thought contingent behaviors. This proposal is based on the general hypothesis that the quantitative characteristics of sequences of behavior in schizophrenia patients will provide a crucial window into understanding cognition and behavior. To test this general hypothesis, methods derived from nonlinear dynamical and complex physical systems and this simple, computerized choice task will be used to assess the sequential organization of behavior in schizophrenia patients, mood disorder patients, and comparison subjects. The fluctuation of the predictability of the response sequences can be quantified and is used to measure the degree of behavioral disorganization. This proposal will allow the investigators to further develop this simple behavioral task in combination with complex mathematical approaches in order to understand the complex dysregulation that characterizes many facets of schizophrenia patient's cognition. 3 specific aims will be addressed in this proposal: (1) Does clinical state, disorder subtype, and treatment significantly affect the dysregulation of behavioral sequences in schizophrenia patients? (2) Is the dysregulation of behavioral sequences specific to schizophrenia? (3) To what extent is the dysregulation of behavioral sequences influenced by changing the feedback (i.e. reinforcement) provided to the subject? The goals of the proposed studies are to clarify the utility of the simple choice task in conjunction with measures derived from dynamical systems theory in order to gain insight into the fundamental characteristics of cognition and behavior in schizophrenia.